Conventionally, a circuit board interconnection structure, in which electrodes provided on a surface of a circuit board are directly joined to electrodes provided on a surface of another circuit board, is known to use an anisotropic conductive film (ACF). An ACF is a mixture containing a reinforcing resin including thermoset resin and conductive particles dispersed uniformly in the reinforcing resin, that is molded into a film. Use of an ACF enables easier interconnection between fine-pitch boards.
An ACF is commonly used in FOG (film-on-glass) applications in particular, in which a FPC (flexible printed circuit) with driver ICs and other components mounted thereon is connected to a circuit board for an LCD (liquid crystal display) panel comprising a glass substrate and transparent electrodes.
However, in a circuit board interconnection structure which uses an ACF, there is increased electrical resistance and less reliable connection, since electricity is conducted between the electrodes by mere contact between the conductive particles and the electrodes. Therefore, a proposal has been made to use solder particles as the conductive particles, so that the electrodes are connected, not only by mere contact between the conductive particles and the electrodes, but also by soldering enabled between the electrodes (c.f., Japanese Laid-Open Patent Application No. 2007-149815).